1. the 12mp sensor form the D3s
2. the 24mp sensor from the D3x
3. the same same sensor as the forthcoming D4
4. "other"

My own view is that it's too late in the day for either 1. or 2. (especially 2. - this should already have happened 2 years ago if it was going to). Although personally I would still buy 1. for the right price.

3. seems possible, but if this were Nikons intention, it would make sense to delay it until some time after the D4 release (i.e. follow same schedule as D3 -->
D700).

That leaves 4. I'm guessing this is the correct one. 20mp, noise performace similar to D700.